1. Field of the Invention
The present invention relates to an apparatus for preventing a stitching from raveling from the sewn end side on forming a double chain stitch in a cloth by a sewing machine.
2. Description of the Prior Art
This kind of stitching ravel preventing device is used in a sewing machine having at least one needle moving vertically, and a looper oscillating almost horizontally between the forward position and backward position across the needle, in which the double chain stitch is formed in the cloth after a thread triangle is formed by a loop-shaped needle thread consecutive to the needle via the looper from the cloth and a looper thread along the looper via the looper eyelet from the cloth by collaboration of the needle and looper.
By this sewing machine, when a stitch, for example, JISL0120 stitch type 406, is formed, if the looper thread is pulled from the sewn end side of the stitching, the stitching is raveled out. As an apparatus for preventing a stitching from raveling, it is disclosed in Japanese Laid-open Patent No. 9-225163 that the construction comprises such a sewing machine, looper thread engaging means, a looper thread cutter and a thread cutter.
A looper thread engaging means forms a looper thread loop consecutively from the cloth at the engaged portion by driving the sewing machine in a state engaged within the longer thread consecutive to the looper from the cloth by moving when the looper is located at the forward position. The looper thread cutter cuts off the looper thread loop at the engaged portion. The thread cutter cuts off the loop-shaped needle thread consecutive to the needle via the looper from the cloth and the looper thread consecutive to the looper from the cloth between the cloth and the looper
According to such a construction, when nearing the finish of sewing on the double chain stitch formed in the cloth, it makes the looper thread engaging means engage with the looper thread consecutive to the looper from the cloth. In this state, the sewing machine is driven for one stitch, and the looper thread loop consecutive from the cloth is formed at the engaged portion, and then the looper thread loop at the engaged portion is cut off, and afterward, or at the same time, the loop-shaped needle thread consecutive to the needle through the looper from the cloth and the looper thread consecutive to the looper from the cloth are cut off between the cloth and the looper.
In such a conventional ravel preventing method, however, since the moving distance of the looper thread engaging means cannot be defined, the length of the looper thread loop formed by the looper thread engaging means cannot be changed, and therefore the length of the thread end left over in the cloth by the looper thread cutter could not be changed.